The present invention relates to a pattern formation method for use in fabrication process or the like for semiconductor devices.
Recently, in the fabrication process for semiconductor devices, the resolution of a resist pattern obtained by lithography has been further refined in accordance with increase of the degree of integration of semiconductor devices. In particular, in a resist pattern having an opening (a hole) for forming a contact hole, the contrast is lowered when the conventional photolithography is employed, and hence, it has become difficult to obtain a desired shape.
Therefore, for forming a fine contact hole pattern through the photolithography, a method in which an opening of the contact hole pattern is shrunk by forming a water-soluble film including a crosslinking agent over a resist pattern previously formed and causing a crosslinking reaction between the resist pattern and the water-soluble film with heat used as a catalyst by using an acid remaining in an unexposed portion of the resist pattern has been proposed (see, for example, T. Ishibashi et al., “Advanced Micro-Lithography Process with Chemical Shrink Technology”, Jpn. J. Appl. Phys., Vol. 40, 2001, pp. 419-425).
Now, a pattern formation method employing the conventional chemical shrink method will be described with reference to FIGS. 15A through 15D and 16A through 16C.
First, a positive chemically amplified resist material having the following composition is prepared:                Base polymer: poly(2-methyl-2-adamantyl acrylate-methacrylic acid) . . . 2 g        Acid generator: triphenylsulfonium nonaflate . . . 0.06 g        Solvent: propylene glycol monomethyl ether acetate . . . 20 g        
Next, as shown in FIG. 15A, the chemically amplified resist material is applied on a substrate 1, so as to form a resist film 2 with a thickness of 0.4 μm.
Then, as shown in FIG. 15B, the resist film 2 is subjected to pattern exposure by irradiating with exposing light 3 through a mask 4 by using an ArF excimer laser stepper having numerical aperture of 0.60.
After the pattern exposure, as shown in FIG. 15C, the resist film 2 is subjected to post-exposure bake (PEB) at a temperature of 105° C. for 90 seconds.
Next, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer) for 60 seconds. Thus, as shown in FIG. 15D, an initial resist pattern 2a with an opening diameter of 0.20 μm made of an unexposed portion of the resist film 2 is obtained.
Subsequently, as shown in FIG. 16A, a water-soluble film 5 including a crosslinking agent having the following composition is applied over the substrate 1 including the initial resist pattern 2a by spin coating:                Base polymer: poly(vinyl alcohol) . . . 2 g        Crosslinking agent: 2,4,6-tris(methoxymethyl)amino-1,3,5-s-triazine . . . 0.2 g        Solvent: water . . . 30 g        
Then, as shown in FIG. 16B, the water-soluble film 5 is annealed at a temperature of 130° C. for 60 seconds, so as to cause a crosslinking reaction between the sidewall of the opening of the initial resist pattern 2a and a portion of the water-soluble film 5 in contact with the sidewall.
Next, as shown in FIG. 16C, a portion of the water-soluble film 5 not reacted with the initial resist pattern 2a is removed. In this manner, a resist pattern 6 with an opening diameter of 0.15 μm made of the initial resist pattern 2a and a remaining portion 5a of the water-soluble film 5 obtained through the crosslinking reaction with the sidewall of the initial resist pattern 2a can be obtained. Thus, the opening diameter of the resist pattern 6 is shrunk to 0.15 μm as compared with that of the initial resist pattern 2a of 0.20 μm.
However, the resist pattern 6 obtained by the conventional pattern formation method is disadvantageously in a poor shape as shown in FIG. 16C. When the resist pattern 6 is thus in a poor shape, a pattern of a member to be etched in subsequent etching is also in a poor shape, which causes a serious problem in fabrication of semiconductor devices. Although a positive chemically amplified resist material is used for forming the resist film 2, such a pattern failure is caused also when a negative chemically amplified resist material is used.
In other words, a pattern of an etching target member obtained by using the resist pattern 6 in a poor shape is also in a poor shape, and therefore, productivity and yield in the fabrication process for semiconductor devices are disadvantageously lowered.